1. Field of the Invention
The present invention relates to supports for a photographic printing paper having suitable physical and photographic properties as supports for a photographic printing paper.
2. Description of the Prior Art
Natural paper hitherto widely used as a support for a photographic printing paper has excellent stiffness, shape retention, adhesion to a photographic layer (e.g., a photographic light-sensitive layer), etc.
The use of natural paper as a support, however, has the disadvantages in that expensive paper having a low impurity content must be used so that the photographic properties of the photographic printing paper as a final product are not deteriorated. This results in an increase in the cost of the final product and, moreover, the quality stability of the product is poor and the operation efficiency is low since a long peiord of time is needed in washing and drying due to the water adsorption property of paper, development and print processing solutions are deteriorated rapidly, and the dimensional stability with changes in humidity is poor.
On the other hand, supports of a synthetic paper, a synthetic resin film, etc., do not have the above disadvantages of a natural paper support, do not absorb water and enable rapid development and printing to be effected.
However, the supports of a synthetic paper, etc., have the following disadvantages; deterioration preventing agents and antistatic agents incorporated in the synthetic resin film of the synthetic paper or coating agents, etc., coated on the surface thereof so as to increase the printing properties permeate through the photographic layer, thus causing discoloration after a long period of time; the surface luster as a photographic printing paper is poor; the adhesion between the support and the photographic layer is poor and the photographic layer is easily peeled off; the shape retention is poor since a synthetic paper itself is not rigid; since a synthetic paper is less stiff in comparison with natural paper having the same thickness and is not subject to expansion and contraction due to changes in temperature, when a photographic layer coated on the surface of a synthetic paper support expands or contracts due to changes in temperature, the synthetic paper support is pulled by the photographic layer and thus the photographic printing paper is easily bent; since heat-rolling can not be applied, a support having a smooth surface must be used for obtaining a photographic layer having a smooth surface, but the surface of a synthetic paper is uneven, etc.